The present invention relates to a cell line that can be grown in serum-free culture and in suspension culture without a carrier, and to production of a vaccine using said cell line. More particularly, the present invention relates to establishment of a cell line that can be grown without using serum and that can be grown in suspension culture without need of the cells to be adhered to any carrier, and a process for producing a vaccine with said cell line.
In general, for production of a vaccine, there are widely used a growing chicken egg, a mouse brain, or primary cells or established cell lines from various animals such as chicken or ape. However, these conventional techniques involve various problems as mentioned below.
First, the use of a growing chicken egg necessitates management of chicken breeding, management of fertilized eggs to be adjusted to a vaccine production schedule, and laborious procedures including extensive purification for completely removing components derived from egg proteins while production. It is also problematic in view of animal protection.
Also in case of established cell lines, fetal calf serum as a cell growth factor must be added. However, its quality might vary among commercial products and it has a risk of contamination with mycoplasma, virus, or infectious proteins such as prion, and hence strict control of quality is required. Thus, a high-quality fetal calf serum such as one produced in New Zealand needs be used but is so costly that renders it unsuitable for production in industrial level.
Also among established cell lines where various kinds of viruses can be propagated, MDCK (Madin Darby Canine Kidney) cells are widely used in laboratory level (Proc. Soc. Exp. Biol. Med., 122, pp.931-935 (1966)). However, MDCK cells are much inclined to adhere to walls. Thus, the use of MDCK cells for an industrial large-scale culture is, due to its need for a large amount of culture medium, a culture vessel or a carrier for culture with a vast area, is disadvantageous in that: (1) it is extremely costly for equipment or a carrier; (2) it needs a step for removing cells adhered to a carrier and thereby some loss of cells is produced while recovery; and (3) cells are damaged due to contact between carriers (beads) according to culture conditions. Thus, it is not practical to use directly MDCK cells for vaccine production in view of cost and equipment.
Consequently, there has been a demand for establishing a process for producing a vaccine in a low-cost, highly safe and stable manner.
Under the circumstances, in order to obviate the disadvantages of the prior art as stated above, the present inventors have kept on investigating. As a result, the present inventors have established a novel cell line which can be grown without fetal calf serum and in suspension culture for enabling tank culture on the production scale and does not need any carrier in suspension culture. The present inventors also established a novel process for producing a vaccine without fetal calf serum to thereby enable providing a vaccine with low cost and high safety, and thus the present invention has been completed.